When a number, letter of the alphabet or special character is read from an input device into main computer storage or is moved from one location to another, the character is stored using its assigned bit configuration. Once a character or bit configuration has been stored in a location in main computer storage, it will remain in that location until another character is placed in the same location.
This feature of main computer storage has two important consequences. First, once data is placed in a location in storage, it will remain there until changed. This allows the program to reference the data for any processing which might be required while the program is being executed.
Second, since data which is moved to or read into a particular location in storage replaces the data which was stored there, a single set of instructions in a computer program which reference particular locations in main computer storage can be used to process many different records which would each be stored in the same storage locations as they are processed. This ability enables a computer programmer to write one sequence of instructions which can process hundreds or thousands of different records.
Figure 4-10 illustrates the processing that occurs as a series of area codes are entered into computer storage from a computer terminal. The first area code, 212, is entered from the terminal and is stored at storage locations 6000, 6001, and 6002. The field, once in storage, would then be processed as required.
When the second area code, 714, is entered from the terminal, it is also stored in storage locations 6000, 6001, and 6002. It replaces the value 212 which was previously stored in these locations. Area code 714 can then be processed by the same instructions which processed area code 212.
Posts Tagged ‘Storage Computer’
Use of main computer storage
Saturday, August 28th, 2010Executing Instructions on a computer
Monday, August 23rd, 2010The execution of an Instruction on the computer system involves the control unit of the CPU “fetching,” or obtaining, the instruction from main computer storage and placing the instruction in an instruction register. An instruction register is nothing more than a storage area within the control unit of the CPU which can store a single Instruction at a time.
The control unit will also fetch any data required for the execution of the Instruction and place the data in special “registers” which can be referenced by the arithmetic/logic unit of the CPU.
The arithmetic/logic unit of the CPU is then given control. It will per. form the actual execution of the instruction and store the answer in another register.
The control unit will then place the answer into main computer storage.